Air conditioning apparatus



June 28, 1966 c. w. PARCE 3,257,816

AIR CONDITIONING APPARATUS Filed Jan. 2, 1964 32 3 4 3| 0241M PA/vF/LTEE INVENTOR g Ckar/er/Z a/ce Q E 5 5 :5

BY 714m 014.) kemafi: g mma.

ATTORNEYS United States Patent This invention relates to airconditioning systems, and more particularly to systems providingconditioned air to an environmental room on a continuous basis withouthaving to shut down the system for defrosting of the cooling coils.

Where air must be conditioned below 32 F., and especially dehumidifiedbelow a dew point of 32 F., it is wellknown that frost will accumulateupon the cooling coils of the conditioning system, thereby insulatingthe coil and restricting the air flow causing a loss of efficiency inthe conditioning system and lOSs of control of desired conditions. Atsuch times as frost forms upon the cooling coils, it is imperative thatit be completely removed with a minimum amount of down time for theconditioning system while maintaining a precise control of theenvironmental room. The present invention contemplates an airconditioning system that permits defrosting while precisely conditionedair is delivered on a continuous basis.

An object of this invention is, therefore, to provide an apparatus forconditioning air, particularly when the air must be conditioned to atemperature below its dew point whether the dew point be above or belowthe freezing point of water.

Another object of this invention is to provide an apparatus which willallow air that has been conditioned below its dew point to be deliveredon a continuous basis without shutting down the conditioning system toremove accumulated frost that will have formed upon the cooling coilsduring operation.

Another object is the provision of an apparatus and control forconditioning air that utilizes independent cooling units operating inclose conjunction with one another to provide a continuous flow ofconditioned air within very close tolerance of temperature and humidity.

Other objects, advantages and capabilities of the invention will becomeapparent from the following description taken in conjunction with theaccompanying drawings showing only a preferred embodiment of theinvention.

In the drawings:

. The figure shows a diagrammatic view of a preferred and practicalembodiment'of an air conditioning system according to this invention.

Referring to the drawing, wherein like reference characters designatecorresponding parts throughout the figure, the air conditioning chamberis generally indicated by reference numeral and comprises a return airfilter 11 mounted in the lower end of the chamber '10 through which airis re-circulated into the system to be reconditioned.

To provide cooling of the air, chamber 10 has mounted therein twoseparate cooling units 12, 13 which may be mounted, as shown in thedrawing, in a spaced vertical relation. Chamber walls 14 of the coolingunits 12, 13 may, if desired, have a hollow core and be filled with asuitable insulation (not shown) to prevent excessive heat transfer fromthe outside ambient air through the walls 14.

The lowermost cooling unit, designated by numeral 12, comprises an airinlet opening 15 and an air discharge opening 16 which allows air, beingdrawn in through filter 11 and opening 15, to be circulated over coolingcoil 17 and conditioned a desired amount before being discharged throughopening 16. The damper system, comprising a pair of dampers 18a and 18b,is adapted to close over the openings 15 and 16 respectively to preventair from entering cooling unit 12 for reasons later to be discussed, and

therefore, the air being unable to pass through unti 12 must passthrough the by-pass plenum 19 without being conditioned by cooling unit12.

Within the bottom panel, or lower wall 21 of cooling unit 12, is a drainpan defrost heater 22 comprising a plurality of resistance heatingcoils, indicated by 22a and 22b, which, upon energization at desiredtimes, will impart heat to interior portion 23 of the wall 21 to removeany ice that may form in the integral drain pan 23a which is soconstructed to effect removal of water whenever cool ing coil 17 isdefrosted and is provided with a suitable drain opening (not shown) toallow exit of the melted frost. Suitably embedded within coil 17 areinternal resistance heating elements, denoted as 17a, which melt anyaccrued frost upon the coil 17 which tends to impede the travel of airtherethrough.

Cooling unit 13 is mounted generally vertically of the cooling unit 12and the two units are basically identical in construction, andespecially this is so with respect to the defrosting systems. The unit13 comprises an air inlet opening 24 and an air discharge opening 25which allows air moving upwardly in the by-pass plenum 1? to flow overcooling coil 26 at such times as the dampers 27a and 27b may be in anopen position, thereby blocking all or a portion of the by-pass plenum19 and necessitating the flow of air through chamber 13 and over coil26.

Located upstream from the conventional centrifugal blower 28 anddischarge opening 29 is an electric resistance heating element 31suitably placed to provide the conditioned air from the plenum '19 witha degree of reheat that may be deemed to be proper at the time. Thefunction of the heater 31 and its operation will be later described, butsufiice it to say that the heater 31 provides reheat to the conditionedair which, after passing through the cooling chamber 12 or 13, may havebeen cooled more than the desired degree due to cooling required fordehumidification, or it may provide heat to raise the temperature of theenvironmental room,

If a particular conditioning application or environmental room calls forthe conditioned air to have a certain amount of humidification over andbeyond that of the ambient air, or if in cooling the air in one of thecooling units 12 or 13 the humidity is lowered, then sufficienthumidification may be supplied by automatically injecting steam into theair discharged from discharge opening 29 from steam line 32 through theautomatic modulated steam valve 33. It should be noted that the steammust be injected into chamber 10 beyond the vicinity of the coolingunits 12 and 13 to prevent the build-up of ice about the walls andcooling coils 17 and 26 of the cooling units when operating below 32 F.In order to accomplish this purpose a specially designed distributorduct 34 is installed to provide proper distribution of the admittedsteam to the discharge air flowing through discharge opening 29. By theprovision of modulating steam valve 33 and specially designeddistributor duct 34 the steam for humidification will be evenlydistributed so it will mix with the condi-- tioned air flowing out ofdischarge 29 thereby providing a highly precise amount of humidificationfor a wide range of operating conditions. The proper distribution of thesteam is accomplished by the provision of a duct 34 located just belowthe discharge opening 29 and by a perforated steam pipe 35, whichintroduces the correct amount of steam into the duct 34. The duct 34 andpipe 35 normally extend the full width of the discharge opening 29 inorder that the steam flowing through duct opening 34a becomes entrainedwith air flowing out of the conditioning units which, at the time thehumidifier is operating, is below the saturation point. If it is desiredthat the humidifier be located other than directly below and in front ofthe discharge opening 29, it may be equipped with a small blower (notshown) to blow room air over the top of the duct 34 to entrain thesteam.

For automatic control of the present conditioning system there isprovided an electronic temperature controller 36 and an electronichumidity controller 37, both of conventional design and moreconveniently called thermostat and hygrostat respectively. To indicatethe environmental room temperature a temperature sensitive sensor 38 isplaced at a convenient location and is connected by an electronic lead39, or any other suitable information transmission means, to thermostat36. In a similar manner the relative humidity of the environmental roomis conveyed by a humidity sensor 41 through line 42 to the hygrostat 37.The room humidity sensor 41 should preferably be placed in or withinclose proximity with the return air stream. Such a location may bewithin the chamber 10 behind filter 11 in order that a precise readingof the humidity of the return air may be had so as to closely modulatethe steam injection from valve 33 if increased humidity is called for.When a reduction of humidity is required by conditions of theenvironmental room the humidity sensor 41 indicates to the hygrostat thedegree of dehumidification needed.

To operate the pair of damper doors 18a and 18b of cooling unit 12,there is provided, as shown schematically in the figure, an electronicmotor 43 responsive to control from thermostat 36. Additionally, anelectric motor 44 that is responsive to control from hygrostat 37 isprovided to operate the dampers 18a, 18b in close conjunction withtemperature responsive motor 43. To combine the outputs from motors 43,44 into a workable damper control, a differential gearing system 45differentially combines the outputs from motors 43, 44 and causes driveshaft 46 and damper door linkages 47a, 47b to move in a manner suitableto modulate the damper doors 18a, 1812 open and shut about pivotalhinges 48a, 48b in whatever degree of movement is necessary to achieve adesired condition in the environmental room.

The damper doors 27a, 27b of cooling unit 13 are Operated in a mannersimilar as the damper doors 18a, 18b of unit 12, and an identicaloperating mechanism is provided which includes temperature responsivemotor 51 responsive to thermostat 36, humidity responsive motor 52responsive to hygrostat 37, differential gearing system 53, drive shaft54 and damper door linkagesSSa, 55b.

In the present invention motors 43, 44, 51 and 52 are understood to benot limited to any particular type or design of motor as other types ofmotors, whether electric, pneumatic or hydraulic, may be used withequally satisfactory results in controlling damper doors 18a, 18b and27a, 27b.

For automaticallycontrolling cooling units 12, 13 independently of oneanother a central control timer mechanism 56 is provided to periodicallyenergize temperature responsive motors 51, 43 to open damper doors 27a,27b of cooling unit 13 and close damper doors 18a, 18b of cooling unit12 whenever a sufficient amount of frost has accumulated upon coil 17,and in addition the timer will energize the electric defrost heater 22to speed in the rapid removal of frost. The timer 56 has numerous otherfunctions to perform in the overall refrigeration system of the presentinvention as will become evident in the description of a typical cycleof operation.

The cooling coils 17, 26 are supplied with a suitable refrigerantthrough conduit 57, and shutoff valves 58 and 59 are situated betweeninlet 61 and cooling coils 17, 26 respectively. Each valve 58, 59 may beindependently operated upon signal from timer 56 indicating shut downtime for defrosting. The refrigerant, after coursing through the opencooling coil and pre-cooling it (the exact one depends upon theparticular operating cycle at that time) exits through conduit 62.

In operation, assuming the refrigeration system of the present inventionto be initially in a steady state condition, the desired environmentalroom conditions of temperature and humidity are normally preset in theelectrical controller 36 for temperature and the electrical humiditycontroller 37 for humidity. With the damper doors 18a and 18b in theposition shown in the figure and with a suitable refrigerant flowingthrough open valve 58 into cooling coil 17 a portion of the air that isbeing drawn through filter 11 is being conditioned as to humidity andtemperature by flowing through opening 15 across cooling coil 17 andthence out into the plenum 19, where it is mixed with the air flowingthrough the by-pass plenum that has not been forced into unit 12 by thedamper doors 18a, 18b, subsequently directed into blower 28 anddischarged into the environmental room that is to be con ditioned.

If the environmental room temperature rises and additional cooling isrequired the temperature sensitive sensor 38 senses the rise intemperature and transmits this information to thermostat 36 whichcontrols through the timer 56 temperature responsive motor 43. The motor43 will operate throughfdifierentiator gear system 45, draft shaft 46and linkages 47a, 47b to modulate damper doors 18a, 18b open to agreater degree in order to block a greater portion of the partiallyopened plenum 19 or to close it completely. If the plenum 19 is blockedcompletely, then the complete intake flow of air from the environmentalroom is allowed to flow over cooling coil 17. The damper doors willcontinue to modulate until sutficient cooling, as indicated by sensor38, has been obtained to reduce the environmental room temperature tothe desired degree.

When a reduction in humidity is indicated the humidity sensor 41 locatedin the return air duct relays to the hygrostat 37 the present relativehumidity reading of air being returned through the filter 11, thehygrostat 37 operates the humidity responsive motor 44 which in turnmodulates doors 18a, 18b to allow more air to pass over cooling coil 17which will remove moisture from the air by condensing it upon thecooling coils 17.

In the event that a temperature drop in the environmental chamber, asindicated by sensor 38, the thermostat will operate motor 43 to energizethe electrical resistance heating element 31 to provide the temperatureincrease to bring the environmental room to the set conditions. Becausedehumidification also acts to lower the temperature of the air blowingacross the cooling coils there will be normally needed a certain amountof reheat imparted to the air in order that the environmental roomtemperature may be kept constant. This reheat function is provided bythe resistance heating element 31 at such time as the temperature sensor38 indicated that the air undergoing dehumidification is also undergoingan unwanted drop in temperature.

When the environmental room temperature rises due to a high load in theenvironmental room, the refrigeration system will respond to thisincrease in temperature rise by providing greater cooling capacity inunit 12 and it will be seen that a corresponding decrease of humiditywill take place when the air is being passed over the cooling coil .17for temperature reduction. Upon the happening of such a condition thehumidity of the environmental room is brought back to its presetcondition by injecting steam through modulating valve 33 into perforatedpipe 35 and thence into duct 34 and out through opening 34a wherein theinjected steam thoroughly and completely mixes with the conditioned airbeing discharged. The amount of steam to be injected is controlled byhumidistat 37 upon information received by the humidity sensor 41located in the returning air duct.

In the normal course of operations it will be seen that both thehumidity and temperature of the environmental room will tend to changeconstantly necessitating that the air being conditioned must becontinuously and simultaneously conditioned as to both temperature andhumidity. Such continuous conditioning is provided for by theincorporation into the present invention of motor 43 responsive only totemperature and motor 44 responsive only to humidity, both of which actthrough differential gearing system 4 5 which algebraically adds therespective imputs of these two motors and modulates the damper doors13a, 18b to a balanced degree of humidity and temperature. Whenthis'balanced degree does not precisely match the preset conditions ofthe environmental room additional temperature and humidity is suppliedby heater 31 and steam modulating valve 33 respectively. With thismethod of control the damper doors are modulated to position so that thecooling, heating dehumidification and reheat exactly balance theenvironmental room load, and after temperature and humidity conditionscalled for by the precise conditions of the environmental room areachieved the damper doors remain practically motionless until a changein room load whereupon the damper doors shift slightly to balance thenew load.

After cooling unit 12 has been in operation for a period of time underconditions requiring operation below a 32 F. dew point of the chamberair, and especially when the unit 12 has been conditioning air that hasa high relative humidity, the water condensed out of the air passingthrough the cooling coil v17 will have accumulated as frost about thetubes of the coil, thereby limiting the volume of air that may pass, andthus the efficiency of the cooling coil is impaired. Periodically thecentral control timer 56 will close down cooling unit 12 and opencooling unit 13 in order that the accumulated frost may be removed fromcoil 17. The time interval between frost removals may be preset intotimer 56 or the timer may be sophisticated enough to have programmedinto it a defrosting schedule that would be dependent upon the operatingtemperature and humidity conditions of the cooling chamber then inoperation. The timer 56 also pre-cools the defrosted coil aftertermination of the defrosting period by opening a refrigerant controlvalve 59.

At the desired time for defrosting coil 17, assuming unit 12 is inoperation, the timer will first open refrigerant control valve 59 toadmit refrigerant to coil 26 of unit 13. Because the idle coil ispre-cooled it is possible to shift the conditioning load to unit 13without any loss of efficiency. Timer 56 also operates temperature motor51 and humidity motor 52 to open damper doors 27a, 27b to allow\the airflowing through plenum 19 to be admitted to the unit 13. Simultaneouslythe damper doors 18a, 1812 are modulating shut at generally the samerate doors 27a, 2% are opening so as not to over or under condition theair.

Once damper 13a, 1812 have completely shut, valve 58 is closed toprevent refrigerant from flowing through coil 17 and the defrost heatersystem 22 is automatically turned on by the timer 56 to apply heat tochamber 12 and coil 17 for the purpose of melting frost. The heatersremain on until the coil is completely defrosted as determined bythermostat sensing element (not shown) located within the confines ofcoil 17. Once the frost is melted and the water has drained from drainpan 23 the heaters are turned off by timer 56 which in turn opens valve58 to reduce the temperatureof'coil 17 in a manner similar to thatdescribed for coil 26 and unit 13.

At the end of the pre-set cycle the timer 56 will act to shut valve 5 9and modulate open doors 18a, 181; and

simultaneously close doors 27a, 27b. The frost that has' accumulated inunit 13 during the operation while unit 12 was being defrosted will beallowed to melt naturally and have the water drained off through a drainin the bottom of the unit similar 'to the drain pan 23 of unit 12. Or inthe alternative it is within the scope of this invention that defrostheaters may be provided in the bottom wall of unit 13 in a mannersimilar to that of unit 12.

With this method of control the damper doors of the cooling units 12,113 are continuously modulated to a position so that the cooling,heating, dehumidification,

and reheat exactly balance the room loading. Experience shows that thissystem provides extremely uniform room conditions over extended periodsdue to its ability to match room loads exactly yet promptly adjustitself to any change in room load, and also its ability to provide frostfree cooling. The unique modulating condition system of the presentinvention provides extremely accurate continuous control of temperatureand humidity over ranges of -25 -F. to +125 F. and 20% to relativehumidity.

While I have particularly shown and described 'one particular embodimentof the invention, it is distinctly understood that the invention is notlimited thereto but that modifications may be made within the scope ofthe invention and such variations as are covered by the scope of theappended claims.

What is ciaimed is:

1. In an air conditioning apparatus comprising a housing having an airinlet and an air outlet, first and second cooling units, means forselectively supplying refrigerant to said cooling units, said secondcooling unit being mounted in a spaced vertical relation with respect tosaid first cooling unit and having a common wall therebetween,electrical defrosting means integral with said first cooling unit,by-pass duct means connecting said housing air inlet and air outlet,each of said cooling units having a plurality of air openings, said airopenings being in communication with said duct means, each of saidcooling unitsbeing adapted to be individually and completely isolatedfrom the passage of air which flows through the duct means and saidhousing, a movable damper door mounted in conjunction with each of saidair openings and adapted to control the proportion of air flowingthrough saidd-uct means and said cooling units, means for moving airthrough said housing, heating means associated with the downstreamportion of said by-pass duct means, thermostatic means downstream withrespect to said heating means, hygrostat means upstream with respect tosaid first cooling unit, motive means for adjusting said damper doors,said motive means comprising for each of said cooling units a motorresponsive to said thermostatic means and a motor responsive to saidhygrostatic means and having the outputs of the motors of each coolingunit differentially connected for adjusting said damper doors of therespective cooling unit.

2. In an air conditioning apparatus comprising a housing having an airinlet and an air outlet, first and second cooling units, means forselectively supplying refrigerant to said cooling units, said secondcooling unit being mounted in a spaced vertical relation with respect tosaid first cooling unit and having a common wall therebetween,electrical defrosting means integral with said first cooling unit,by-pass duct means connecting said housing air inlet and air outlet,each of said cooling units having a plurality of air opening-s, said airopenings being in communication with said duct means, each of saidcooling units being adapted to be individually and completely isolatedfrom the passage of air which flows through the duct means and saidhousing, a movable damper door mounted inconjunction with each of saidair openings and adapted to control the proportion of air flowingthrough said duct means and said cooling units, means for moving airthrough said housing, heating means. associated with the downstreamportion of said bypass duct means, thermostatic means downstream withrespect to said heating means, hygrostat means upstream with respect tosaid first cooling unit, humidifier means located downstream from saidsecond cooling unit in said housing for imparting humidification to theconditioned air after discharge, control means responsive to saidthermostatic means and said hygrostatic means, motive means foradjusting said damper doors, said motive means being adapted to becontrolled by said control means to selectively position said damperdoors of one of said cooling units open while maintaining the damperdoors of the other cooling unit closed, said heating means, humidifiermeans and defrosting means being simultaneously responsive to saidcontrol means whereby air flowing through said air conditoning apparatusis conditioned within close tolerances of temperature and humidity on acontinuous basis.

3. In the air conditioning apparatus of claim 2 wherein said means formoving air through said housing comprises, an air blower mountedvertically above said cooling units and being in communication with saidby-pa-ss duct for moving air through said cooling units and said by-passduct,

4. In the air conditioning apparatus of claim 2 wherein said heatingmeans comprises, an electrical resistance heating means being mounted insaid by-pass duct means whereby a controlled amount of reheat isimparted to the discharged air upon energization of the heating means.

5. In the air conditioning apparatus of claim 2 wherein said humidifiermeans comprises a steam injecting and diflusing apparatus to completelyentrain the steam in the discharged conditioned air thereby preventingany dripping of condensate when the apparatus operates at lowtemperatures.

6. In an air conditioning apparatus comprising an air outlet, first andsecond cooling units, means for selectively supplying refrigerant tosaid cooling units, said second cooling unit being mounted in a spacedvertical relation with respect to said first cooling unit and having acommon wall therebetween, electrical defrosting means integral with saidfirst cooling unit, by-pass duct means connecting said housing air inletand air outlet, each of said cooling units having a plurality of airopenings, said air openings being in communication with said duct means,a movable damper door mounted in conjunction with each of said airopenings and adapted to control the proportion of air flowing throughsaid duct means and said cooling units, an air blower mounted verticallyabove said cooling units and being in communication with said by-passduct for moving air through said cooling units and said by-pass duct, anelectrical resistance heating means associated with the downstreamportion of said bypass duct means whereby a controlled amount of reheatis imparted to the discharged air upon energization of the heatingmeans, thermostatic means downstream with respect to said electricalresistance heating means, hygrostat means upstream with respect to saidfirst cooling unit, humidifier means located, downstream from saidsecond cooling unit in said housing for imparting excess humidificationto the conditioned air after discharge, said humidifier means comprisinga steam injecting and diffusing apparatus, control means responsive tosaid thermostatic means and said hygrostatic means, motive means foradjusting said damper doors, said motive means comprising for each ofsaid cooling units a motor responsive to said thermostatic means and amotor responsive to said hygrostatic means and having the outputs of themotors of each cooling unit differentially connected for adjusting saiddamper doors of the respective cooling unit, said heating means,humidifier means and defrosting means being simultaneously responsive tosaid control means whereby air flowing through said air conditioningapparatus is conditioned within close tolerances of temperature andhumidity on a continuous basis.

7. A method of conditioning air to a temperature below the dew point ofthe air being conditioned comprising the steps of sensing thetemperature of air in an environmental chamber, passing the air into apassageway, sensing the humidity of the air being passed into saidpassageway, adjusting air blocking means associated with a first coolingunit in said passageway in response to the temperature and humiditysensings of the air to block a portion of the flow of air in saidpassageway, passing the blocked portion of the air through a firstcooling coil in said first cooling unit reducing the temperature andhumidity of the air, then mixing the air having reduced temperature andhumidity with the air flowing in said passageway, then passing the mixedair past a closed second cooling unit, periodically at a predeterminedtime admitting refrigerant to a cooling coil in said second coolingunit, then closing said first cooling unit air blocking means andsimultaneously adjusting passageway air blocking means of said secondcooling unit to block a portion of the flow of air in said passageway,then passing a portion of the air through said second cooling coilreducing the temperature and humidity of the air, then mixing the airhaving reduced temperature and humidity with the air flowing in saidpassageway, stopping the flow of refrigerant in said first cooling coiland defrosting said first cooling coil during the time said secondcooling coil is in operation.

8. A method of conditioning air to a temperature below the dew point ofthe air being conditioned comprising the steps of sensing thetemperature of air in an environmental chamber, passing the air into apassageway, sensing the humidity of the air being passed into saidpassageway, adjusting air blocking means associated with a first coolingunit in said passageway in response to the temperature and humiditysensings of the air to block a portion of the flow of air in saidpassageway, passing the blocked portion of the air through a firstcooling coil in said first cooling unit reducing the temperature andhumidity of the air, then mixing the air having reduced temperature andhumidity with the air flowing in said passageway, then passing the mixedair past a closed second cooling unit, periodically at a predeterminedtime admitting refrigerant to a cooling coil in said second coolingunit, then closing said first cooling unit air blocking means andsimultaneously adjusting passageway air blocking means of said secondcooling unit to block a portion of the flow of air in said passageway,then passing a portion of the air through said second cooling coilreducing the temperature and humidity of the air, then mixing the airhaving reduced temperature and humidity with the air flowing in saidpassageway, stopping the flow of refrigerant in said first cooling coiland defrosting said first cooling coil during the time said secondcooling coil is in operation, discharging the conditioned air into anenvironmental chamber and immediately thereafter causing finely dividedparticles of steam to become entrained in the air to providehumidification.

References Cited by the Examiner UNITED STATES PATENTS 2,001,704 5/1935Bulkeley 20 2,207,714 7/1940 Bulkeley 165-2O 2,388,210 10/1945 Hanson etal. 165-21 2,389,440 11/1945 Kucher 16521 3,063,253 11/1962 Dickson etal. 62-276 X 3,065,608 11/1962 Arz'berger 6280 3,091,942 6/1963 Dicksonet al, 62-8O ROBERT A. OLEARY, Primary Examiner. MEYER PERLIN, Examiner.

W. E. WAYNER, Assistant Examiner.

7. A METHOD OF CONDITIONING AIR TO A TEMPERATURE BELOW THE DEW POINT OF THE AIR BEING CONDITIONED COMPRISING THE STEPS OF SENSING THE TEMPERATURE OF AIR IN AN ENVIRONMENTAL CHAMBER, PASSING THE AIR INTO A PASSAGEWAY SENSING THE HUMIDITY OF THE AIR BEING PASSED INTO SAID PASSAGEWAY, ADJUSTING AIR BLOCKING MEANS ASSOCIATED WITH A FIRST COOLING UNIT AND SAID PASSAGEWAY IN RESPONSE TO THE TEMPERATURE AND HUMIDITY SENSING OF THE AIR TO BLOCK A PORTION OF THE FLOW OF AIR IN SAID PASSAGEWAY, PASSING THE BLOCKED PORTION OF THE AIR THROUGH A FIRST COOLING COIL IN SAID FIRST COOLING UNIT REDUCING THE TEMPERATUERE AND HUMIDITY OF THE AIR, THEN MIXING THE AIR HAVING REDUCED TEMPERATURE AND HUMIDITY WITH THE AIR FLOWING IN SAID PASSAGEWAY, THEN PASSING THE MIXED AIR PAST A CLOSED SECOND COOLING UNIT, PERIOCIALLY AT A PREDETERMINED TIME, ADMITTING REFRIGERANT TO A COOLING COIL IN SAID SECOND COOLING UNIT, THEN CLOSING SAID FIRST COOLING UNIT AIR BLOCKING MEANS AND SIMULTANEOUSLY ADJUSTING PASSAGEWAY AIR BLOCKING MEANS OF SAID SECOND COOLING UNIT TO BLOCK A PORTION OF THE FLOW OF AIR IN SAID PASSAGEWAY, THEN PASSING A POR- 